Conventional processes for testing TAB parts includes logically isolating the TAB parts to be tested from the printed circuit boards (PCB's) on which they are mounted. Such testing process has proven to be less than completely desirable, in that the PCB, other components, integrated circuits (IC) or dies mounted on the PCB can cause the TAB part to incorrectly test as defective.
One attempted solution to this problem has been to test the TAB part while still mounted onto the PCB. However, the parasitic interactions between this TAB part and the PCB and the other components thereon, may result in incorrect test readings, due to the failure of other components rather than the failure of the part being tested. Such testing errors result in obvious serious disadvantages, among which is the financial loss due to the "scrapping" of fully functional parts, or components.
Wherefore, it is highly desirable to have a new and improved TAB frame and method of testing the same, which minimize, if not completely eliminate the undesirable interactions between the TAB parts being tested and the other components on the same PCB.
Another attempted solution has addressed the above problem, and consists of desoldering the TAB part to be tested from the PCB, and to test this part by probing its outer leads. However, during the desoldering process or during subsequent handling of the TAB part, the TAB leads generally bend, and become non-probeable and thus non-testable.
Wherefore, it is highly desirable to have a new and improved TAB frame and method of testing the same, which not only minimize or completely eliminate the undesirable interactions between the TAB parts being tested and the other components on the same PCB, but which further minimize, if not entirely eliminate the undesirable bending of the TAB leads, as well as the need for desoldering the TAB part from the PCB.
In order to solve this problem, another common attempted solution has been to use a probe card to probe the top of the TAB leads above the die. This technique presents several problems, among which are the following three concerns. The first concern is that many failures that exist may be overlooked or ignored because the force of the probes onto the TAB inner leads of the faulty part tends to hold broken leads together during the test. Hence, parts which should fail as open actually test good.
The second concerns relates to open circuits on the TAB tape which would not be detected, since the tape itself is neither probed nor tested for failure. Usually, these open circuits occur at the inner lead tape edges. Thus, several tape failures can flow undetected.
The third concern is that in order to establish proper contact, the probes of the probe card would have to entirely penetrate the relatively hard encapsulant layer which coats the inner leads of the part being tested. Generally, in many instances, it would be extremely difficult, if not virtually impossible to ensure the full penetration of all the probes through the encapsulant layer, and thus to guarantee their proper contact with the TAB leads being tested. Obviously, in the miniature environment in which the test is being performed, even a very thin layer of encapsulant between the TAB leads, and the probes would cause incorrect test results.
In some instances the TAB parts that failed during the assembly process are tested to identify the cause of the failure. These parts are typically removed from the TAB tape prior to assembly, and their inner leads as previously described in relation with the testing of the TAB part by desoldering it from the PCB on which it is mounted. Accordingly, similar problems are encountered as discussed above.
Wherefore, it is highly desirable to have a new and improved TAB frame and method of testing the same, which, in addition to minimizing or eliminating the undesirable interactions between the TAB parts being tested and the other components on the same PCB, and in addition to further minimizing or eliminating the undesirable bending of the TAB leads, as well as the need for desoldering the TAB part from the PCB's, permit the detection of open circuits onto the TAB tape, which enable the testing of the TAB tape, and which allow all the probes of the probe card to come in proper contact with the TAB leads.